1. Field of the Invention
The present invention relates in general to a honeycomb panel and a method of producing the honeycomb panel, and more particularly to a honeycomb panel having an opening in which another structural member is fixed, and a method of producing such a honeycomb panel.
2. Discussion of the Prior Art
There is known a brazed aluminum honeycomb panel which a honeycomb core is sandwiched between and brazed to two face plates. An example of such aluminum honeycomb panel is disclosed in laid-open Publication No. 64-44268 of unexamined Japanese Patent Application and laid-open Publication No. 1-143668 of unexamined Japanese Utility Model Application.
Since the aluminum honeycomb panel of the type indicated above is comparatively lightweight, and has relatively high strength and weldability, this honeycomb panel finds applications for automotive vehicle bodies, body structures for railway rolling stock, and architectural structures.
Some of such aluminum honeycomb panels for various structural applications have openings formed for windows or doors, or for piping, wiring and other purposes. Usually, a suitable member such as a frame for supporting a window pane is fixed in such openings, by welding or other suitable means. In addition to such frame member fixed in the openings, another frame member is attached to a peripheral portion of the honeycomb panel, where the panel is connected to some other structural member.
On the other hand, the face plates and the honeycomb core of the aluminum honeycomb panel have extremely small wall thicknesses, for reducing the weight of the panel. Further, a considerable portion of the volume of the honeycomb core interposed between the face plates consists of a void. Accordingly, it is very difficult for the solid portion of the honeycomb core to provide a sufficiently large area for welding thereto the frame member disposed in an opening which is defined by the cut surfaces of the honeycomb cells. Therefore, the honeycomb core does not permit sufficient welding strength of the frame member.
For improving the strength of bonding of the frame member to the aluminum honeycomb panel, welding of a reinforcing member to the outer surfaces of the panel was considered. The provision of such reinforcing member is not desirable particularly where the honeycomb panel is required to have smooth outer surfaces. The reinforcing member is undesirable from the standpoint of weight reduction of the panel. Thus, the honeycomb panel using the reinforcing member for welding the frame member cannot be suitably used for structural members which form a surface of a structure, particularly, for body structures for railway rolling stock and automobiles, Which are required to have smooth surfaces, for reducing air resistance and noises and improved appearance.
There are also known honeycomb panels which have inserts disposed in the cells of the honeycomb core, for improving the strength of the panel, as disclosed in laid-open Publication Nos. 64-25514 and 2-25325 of unexamined Japanese Utility Model and Patent Applications. However, these honeycomb panels are not satisfactory, in terms of the strength of bonding of a frame member or other structural member to the panel.